The invention pertains to a plastic multilayer sheet for making containers meant to be closed by means of a sealed lid.
The present invention also pertains to the production of containers made from this sheet, to be used for foodstuff for instance, and meant to be closed by a lid sealed to their open upper side. These containers are, for example, the boats or pots into which are sold foodstuff such as deserts.
These containers are usually thermoformed from a plastic in sheet form often presenting several layers of different materials such as polystyrene, ethylvinyl alcohol (EVOH) and polyethylene, bound by adhesives.
At present, the lids come in the form of a thin multilayer sheet comprised, for instance, of a sheet of aluminium or of polyester onto which the information meant for the customers is printed, and which is coated, on its side in contact with the container, with a thin layer of polyethylene.
It is by means of this thin layer of polyethylene that sealing of the lid to the lip presented by the container around its open side, is ensured.
When analysing the opening of a container so sealed, it is found that in many cases, this opening is difficult to perform.
Indeed, the lower layer of the lid and the upper layer of the container are both made of polyethylene and are sealed together. For the container to open, it must be possible to break the bond between the two sealed layers.
In some cases, the seal is very difficult to break, and the force that one is brought to excert on the lid often results in the tearing of the lid, hence making it necessary to take hold of the latter by small fragments.
In other cases, the thin polyethylene layer remains sealed to the container while having removed the upper layer(s) of the lid.
This problem of sealed containers has not yet been suitably and definitely resolved. For this reason, the objective of the present invention is to propose a novel solution permitting the production of a seal of the lid that is impervious and sufficiently resistant to the various demands to which it may be subjected during the commercialization of the containers, while permitting the easy removal of the lid without tearing it.